1. Field of the Invention
The embodiments discussed herein relate to a semiconductor module, and particularly to a semiconductor module that includes, in one package, a switching element, a diode, and a control integrated circuit (IC) for electric power conversion.
2. Background of the Related Art
In an electric power conversion inverter circuit or the like, insulated gate bipolar transistors (IGBTs) that are excellent in reducing loss and operating in a high frequency are used as switching elements. Such an IGBT has evolved from a single element to an intelligent power module (IPM) that contains a protection diode (a freewheeling diode) and a control IC including peripheral circuits such as a drive circuit and various types of protection circuits.
FIG. 11 illustrates an exemplary inner configuration of a past IPM.
An IPM 100 illustrated in FIG. 11 forms an inverter that outputs three-phase alternate-current voltage. Thus, the IPM 100 has a positive power supply terminal P, a negative power supply terminal N, and output terminals U, V, and W, and contains six IGBTs 101 to 106. Protection diodes 111 to 116 are provided on the same circuit pattern and are connected to the IGBTs 101 to 106 respectively in an antiparallel manner. Each pair of the IGBTs 101 and 102, the IGBTs 103 and 104, and the IGBTs 105 and 106 are connected in series to make up three sets of arm units, between the positive power supply terminal P and the negative power supply terminal N. Also, intermediate connection portions of the arm units of U, V, and W phases are connected to the output terminals U, V, and W, respectively.
Temperature detection diodes having PN junctions are formed at the centers of the surfaces (emitter terminals) of the IGBTs 101 to 106, with insulating layers in between. Thereby, with regard to the IGBTs 101 to 106, chip temperature that is close to junction temperature can be observed by monitoring temperature-dependent forward voltage of the temperature detection diodes.
Also, the gate terminals of the IGBTs 101 to 106 and the temperature detection diodes are connected to control ICs 121 to 126. The control ICs 121 to 126 control and switch the IGBTs 101 to 106 and flow constant current in the temperature detection diodes in order to detect overheated states of the IGBTs 101 to 106.
Also, the IPM 100 includes a dedicated temperature detection IC 131 that detects case temperature, in addition to the temperature detection ICs that detect chip temperature. This temperature detection IC 131 is provided at a part of an insulating substrate and detects an overheated state of the case of the IPM 100 by detecting the temperature there. A thermistor is generally used as a temperature detection element of the temperature detection IC 131 (for example, refer to Japanese Laid-open Patent Publication No. 2002-184940 (paragraph [0109])), but here the temperature detection IC 131 uses a diode which has the same structure as the temperature detection diodes of the IGBTs 101 to 106 and is formed on a bare chip of the temperature detection IC 131.
FIG. 12 is a circuit diagram illustrating an overheat protection circuit of the past IPM, and FIGS. 13A and 13B illustrate temperature characteristics of the temperature detection diodes, where FIG. 13A illustrates overheat detection voltage in relation to temperature at the time of chip overheat protection, and FIG. 13B illustrates overheat detection voltage in relation to temperature at the time of case overheat protection.
The control ICs 121 to 126 are connected to the IGBTs 101 to 106 respectively, as illustrated in FIG. 12. That is, each of the control ICs 121 to 126 includes an output terminal OUT for outputting gate voltage, a ground terminal GND, an overcurrent detection terminal OC, and an overheat detection terminal OH.
The output terminal OUT is connected to the gate terminal of each IGBT 101 to 106, and the ground terminal GND is connected to the emitter terminal of each IGBT 101 to 106, and the overcurrent detection terminal OC is connected to a current-sense emitter terminal of each IGBT 101 to 106.
In each control IC 121 to 126, the overheat detection terminal OH is connected to a constant current source 141 and an inverting input terminal of an overheat detection comparator 142, and a non-inverting input terminal of the overheat detection comparator 142 is connected to a reference voltage supply 143. Also, the overheat detection terminal OH is connected to an anode terminal of a temperature detection diode 107 of each IGBT 101 to 106, and a cathode terminal of the temperature detection diode 107 is connected to a ground electric potential of the control ICs 121 to 126 via the ground terminal GND.
The constant current generated by the constant current source 141 always flows in the temperature detection diode 107, and forward voltage corresponding to chip temperature of each IGBT 101 to 106 is applied to the inverting input terminal of the overheat detection comparator 142. Here, temperature characteristics of the temperature detection diode 107 is negative as illustrated in FIG. 13A, and the reference voltage supply 143 outputs a voltage VOH1 corresponding to the temperature of 175° C. Thus, the overheat detection comparator 142 outputs a protection operation signal of low level when the chip temperature is lower than 175° C., and outputs a protection operation signal of high level when the chip temperature is equal to or higher than high temperature of 175° C. When this protection operation signal of high level is output, the control ICs 121 to 126 control and turn off all of the IGBTs 101 to 106 simultaneously with outputting an alarm signal from an alarm output circuit.
On the other hand, the temperature detection IC 131 includes a temperature detection diode 132, a constant current source 133, and an overheat detection comparator 134. An anode terminal of the temperature detection diode 132 is connected to the constant current source 133 and an inverting input terminal of the overheat detection comparator 134, and a cathode terminal of the temperature detection diode 132 is connected to the ground. A non-inverting input terminal of the overheat detection comparator 134 is connected to a reference voltage supply 135.
The constant current by the constant current source 133 always flows in the temperature detection diode 132, and forward voltage corresponding to case temperature is applied to the inverting input terminal of the overheat detection comparator 134. Here, the temperature characteristics of the temperature detection diode 132 is negative as illustrated in FIG. 13 (B), and the reference voltage supply 135 outputs a voltage VOH2 corresponding to the temperature of 125° C. Thereby, the overheat detection comparator 134 outputs a protection operation signal of low level when the case temperature is lower than 125° C., and outputs a protection operation signal of high level when the case temperature is equal to or higher than medium temperature of 125° C. When this protection operation signal of high level is output, the temperature detection IC 131 controls and turns off all of the IGBTs 101 to 106 simultaneously with outputting an alarm signal from the alarm output circuit.
However, the past IPM needs to include a dedicated temperature detection IC for the purpose of case overheat detection, and in addition the case overheat is detected at a single spot where the temperature detection IC is located, and thus there has been a problem that overheat is undetectable at other spots.